Polyurethane foams are widely known and used in automotive, housing and other industries. Foam is generally referred to as rigid, microcellular or flexible. Typically, in the preparation of polyurethane foams, a tertiary amine catalyst is used to accelerate the reaction of the polyisocyanate with water to generate carbon dioxide as a blowing agent and to accelerate the reaction of polyisocyanate with polyols to promote gelling. Tertiary amines generally are malodorous and offensive and many have high volatility due to low molecular weight. Release of tertiary amines during foam processing may present significant safety and toxicity problems, and release of residual amines from consumer products is generally undesirable.
Amine catalysts which contain primary and/or secondary hydroxyl functionality typically have limited volatility and low odor when compared to related structures which lack this functionality. Furthermore, catalysts which contain hydroxyl functionality chemically bond into the urethane during the reaction and are not released from the finished product. Catalyst structures which embody this concept are typically of low to moderate activity and, typically, more favorably promote the blowing (water-isocyanate) reaction over the gelling (polyol-isocyanate) reaction. Examples of such structures are included in U.S. Pat. Nos. 4,957,944; 5,071,809 and 5,091,583.
Prior art examples of hydroxy functional tertiary amine catalysts which have selectivity for the gelling (polyol-isocyanate) reaction over the blowing (water-isocyanate) reaction are difficult to find. U.S. Pat. No. 5,143,944 discloses 3-quinuclidinol (3-hydroxyazabicyclo 2.2.2!octane) and its alkoxylated derivatives as catalysts which are selective for the gelling reaction.
Although pyrrolizidines are known to be catalysts for the production of polyurethane foams, they are primarily used as blowing catalysts.
DE 2,040,607 discloses pyrrolizidine (1-azabicyclo 3.3.0!octane) as a polyurethane foaming catalyst which does not influence gelation.
CA 2,061,168 A discloses the preparation and use of substituted pyrrolizidines as polyurethane foaming catalysts. Preparative examples include pyrrolizidines substituted or disubstituted at the 3- and 4-position either with an electron withdrawing group such as cyano or butyl ester or alternatively with aminomethyl functionality.